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Abstract

We investigate the physical properties of a sample of six submillimeter galaxies (SMGs) in the COSMOS field, spectroscopically
confirmed to lie at redshifts z > 4. While the redshifts for four of these SMGs were previously known, we present here two newly
discovered zspec > 4 SMGs. For our analysis we employ the rich (X-ray to radio) COSMOS multi-wavelength datasets. In particular,
we use new data from the Giant Meterwave Radio Telescope (GMRT) 325 MHz and 3 GHz Jansky Very Large Array (VLA) to probe
the rest-frame 1.4 GHz emission at z = 4, and to estimate the sizes of the star formation regions of these sources, respectively. We find
that only one SMG is clearly resolved at a resolution of 0.
6 × 0.
7 at 3 GHz, two may be marginally resolved, while the remaining
three SMGs are unresolved at this resolution. Combining this with sizes from high-resolution (sub-)mm observations available in the
literature for AzTEC 1 and AzTEC 3 we infer a median radio-emitting size for our z > 4 SMGs of (0.
63 ± 0.
12) × (0.
35 ± 0.
05)
or 4.1 × 2.3 kpc2 (major × minor axis; assuming z = 4.5) or lower if we take the two marginally resolved SMGs as unresolved. This
is consistent with the sizes of star formation regions in lower-redshift SMGs, and local normal galaxies, yet higher than the sizes of
star formation regions of local ultraluminous infrared galaxies (ULIRGs). Our SMG sample consists of a fair mix of compact and
more clumpy systems with multiple, perhaps merging, components. With an average formation time of ∼280 Myr, as derived through
modeling of the UV IR spectral energy distributions, the studied SMGs are young systems. The average stellar mass, dust temperature,
and IR luminosity we derive are M ∼ 1.4 × 1011 M , Tdust ∼ 43 K, and LIR ∼ 1.3 × 1013 L , respectively. The average LIR is up
to an order of magnitude higher than for SMGs at lower redshifts. Our SMGs follow the correlation between dust temperature and
IR luminosity as derived for Herschel-selected 0.1 < z < 2 galaxies. We study the IR-radio correlation for our sources and find a
deviation from that derived for z < 3 ULIRGs ( qIR = 1.95 ± 0.26 for our sample, compared to q ≈ 2.6 for IR luminous galaxies
at z < 2). In summary, we find that the physical properties derived for our z > 4 SMGs put them at the high end of the LIR–Tdust
distribution of SMGs, and that our SMGs form a morphologically heterogeneous sample. Thus, additional in-depth analyses of large,
statistical samples of high-redshift SMGs are needed to fully understand their role in galaxy formation and evolution.

Context. Submillimetre galaxies (SMGs) represent an important source population in the origin and cosmic evolution of the most massive galaxies. Hence, it is imperative to place firm constraints on the fundamental physical ...

Context. Submillimetre galaxies (SMGs) in the early Universe are potential antecedents of the most massive galaxies we see in the present-day Universe. An important step towards quantifying this galactic evolutionary ...

We present the first study of the far-infrared (FIR) properties of high-redshift, radio-selected ultraluminous infrared galaxies (ULIRGs) using deep observations obtained with the Spectral and Photometric Imaging Receiver ...

Statistics

Curtin University would like to pay our respect to the indigenous members of our community by acknowledging the traditional owners of the land on which the Perth Campus is located, the Wadjuk people of the Nyungar Nation; and on our Kalgoorlie Campus, the Wongutha people of the North-Eastern Goldfields.Watch our traditional Aboriginal welcome